The invention relates to an alkali metal thermoelectric conversion (AMTEC) device and more particularly to one with improved mechanical strength and higher performance.
Alkali metal thermoelectric conversion devices convert heat directly to electrical energy, using a beta-alumina solid electrolyte member that will conduct sodium ions, but not electrons. This electrolyte member forms a boundary between high and low pressure sodium filled regions. The temperature in the region of the electrolyte is elevated so that the corresponding saturation pressure is greater than the low pressure region. Under these conditions a chemical potential is developed across the electrolyte that drives sodium ions from the high to the low pressure side along ion conduction planes in the crystal lattice. A charge or potential difference is thereby developed across the electrolyte by the positive ions emerging on the low pressure side and excess electrons, released when the neutral sodium ionized, accumulating on the high pressure side.
Electronic conduction layers, that allow the passage of sodium to the surface of the electrolyte, are located on both sides of the electrolyte. These conduction layers are connected through a load and allow the excess electrons accumulating on the high pressure side to move to the low pressure side where they recombine with the excess sodium ions, and in the process perform electrical work on the load. The sodium ion that has passed through the electrolyte and recombined with an electron on the low pressure side, evaporates from the electrolyte surface and is then condensed, collected and pumped back to the high pressure side. Thermal energy is added to the system to replace the generated electrical energy and any heat rejection from the device. U.S. Pat. No. 4,808,240 granted to one of the inventors describes a stacked vapor fed AMTEC module that operates on the principle described herebefore. The beta-alumina used in such devices have mechanical properties susceptible to failure from thermal and mechanical stresses.